The piccolo trumpet is the highest voice in the trumpet family.  Most are pitched in Bb and can be converted to A, often with a second set of included slides.  These are used in orchestras and by solists, and are often found in the brass quintet.  Onece you've mastered the Bb and C trumpet, the piccolo should be your next conquest.  The piccolo's fourth valve allows better pitch in the lower range and additional trill options.  While most piccolo trumpets are designed to be played with the four fingers of the right hand, some fourth valves can be operated by the first finger of the left hand.